1. Field of the Invention
The present invention relates to a Reaction Injection Molding (RIM) method of thermoplastic resin such as polyester, polycarbonate and so on.
2. Description of the Related Art
In a conventional RIM method, a material for thermoplastic resin is mixed with a polymerization catalyst to be injected into a mold, and the material for thermoplastic resin is polymerized in the mold to form a thermoplastic resin molded body.
Japanese Laid-Open Patent Publication No. 127733/1983 discloses an RIM method of nylon as follows. At first, an annular lactam such as .epsilon.-caprolactam is mixed with a polymerization catalyst to make a component (A). Then, an annular lactam is mixed with a polymerization accelerator and an epoxy element to make a component (B). After each of two components (A) and (B) is heated and fused, they are mixed and injected into a mold having high temperature to be polymerized.
As described in detail, the polymerization catalyst of the component (A) includes hydride of alkaline metals or alkaline earth metals, alkylhalide, hydroxide, an organic metal compound and so on. The polymerization accelerator of the component (B) includes terephthaloyl biscaprolactam and so on. Each of the components (A) and (B) is heated and fused at the temperature of 70.degree. C. to 100.degree. C., and then, they are mixed and injected into the mold having the temperature of 100.degree. C. to 200.degree. C.
U.S. Pat. Nos. 4,853,459, 4,778,875 and SAMPE Journal, Vol. 27, No. 1, 1991 disclose an RIM method of polyester or polycarbonate in which an annular carbonate or an annular ester is mixed with a polymerization catalyst such as a metal oxide or an organic metal compound. After that, it is heated, fused and injected into a mold having high temperature to be polymerized by a ring-opening addition-polymerization.
In the above-described molding methods, a reaction of material for thermoplastic resin is occurred before the material for thermoplastic resin is injected into a mold. For example, in Japanese Laid-Open Patent Publication No. 127733/1983, a polymerization reaction begins at the time of heating and fusing since an annular lactam exists with a polymerization catalyst having high-activity in the component (A). In U.S. Pat. Nos. 4,853,459, 4,778,875 and SAMPE Journal, Vol.27, No.1, 1991, a polymerization reaction begins at the time of heating and fusing since an annular material exits with a polymerization catalyst.
When the polymerization reaction begins before the material for thermoplastic resin is injected into the mold, the viscosity of the component at the time of injection increases, and a fluidity of the component in the mold deteriorates. This causes an insufficient molding. In the worst case, the material for thermoplastic resin is resinified before it is injected into the mold.
Furthermore, when a reinforced fiber is arranged in the mold and a resin is impregnated into the reinforced fiber to form FRP, an increase in viscosity prevents thermoplastic resin material from being impregnating into fiber, and a satisfactory strength is not obtained.
To solve the above disadvantages, a polymerization catalyst having low activity is used in order to lower the rate of polymerization. In this case, a low viscosity condition can be maintained for a long time, and fluidity in the mold and impregnation characteristics of the component are improved. However, a polymerization reaction in the mold becomes deteriorated and it takes too much time for molding.